1. Field of the Invention
This invention relates generally to the field drywall construction and more particularly to a system of exterior and interior drywall seams and corners that greatly reduces the amount of time, labor and material required to finish a modern structure.
2. Description of Related Art
The use of gypsum drywall board in modem construction is well known. Manufactured drywall sheets are nailed to studs to form interior walls and ceilings. Before these sheets can be painted or textured, the joints must be taped and sealed with joint sealing compound (drywall mud). Drywall tape is a porous fibrous material, usually paper, which is designed to permanently bond with drywall mud.
Taping also known as stringing) is a tedious process. First, mud and tape must be applied by hand or dispensed with a tool known as a bazooka. The worker rolls and glazes the tape while the mud is wet. As the tape strings out, it has a tendency to pull in the direction of motion. After the tape is applied, it is coated with additional mud and the edges are feathered with a wide blade drywall knife to form a smooth transition between the seam and the wall. The mud is then allowed to dry, typically overnight. Next, the seam is sanded, recoated with mud, dried and sanded again. The process is repeated if necessary until a smooth seam is produced.
Corners present a special problem. Inside corners are finished using drywall tape in much the same manner as flat joints. Outside corners are typically finished with corner beads.
Corner beads are either sharp edged or rounded nose, also known as "bullnose." These are used on exterior corners at windows and other openings. To use a standard corner bead, it first must be cut from a standard length of 8 feet or 10 feet. The bead is nailed into position using short nails approximately every foot. The worker must: 1) keep the bead plumb or level, and 2) keep the bead at the proper angle to prevent slipping too far to one side or the other. If this latter condition occurs, a "shiner", as it is called in the trade, results. This is where the bead is too far toward one side of the corner making the other side flange hard to coat.
Once the bead is installed, the worker must "first coat" the bead. This means to coat it with mud for the first time. This is very labor intensive, and it uses a large amount of mud. The bead projects outwardly from the corner. Accordingly, when first coat is applied a wedge of mud is formed which is thickest at the bead and tapers out to meet the wall. After the first coat, the mud is allowed to dry. Drying takes about a day.
After the "first coat" is dry throughout the building, the worker has to sand this first coat of mud and clean all the metal edges. This is especially difficult with bullnose bead. After the "first coat" is sanded, the worker proceeds to "second coat" the bead repeating the entire process again and waiting another day to dry. The worker finally must again sand the bead carefully looking for imperfections, and touching these up. At this point, the bead is ready for texture or paint. The entire process uses considerable mud, and is very labor intensive, especially the sanding. In terms of total construction time, it requires two to three days to complete all the corners of a typical residence.
An alternative to fixed corner beads, especially for corners that do not meet at 90 degrees is a product known as "flex bead." Flex bead consists of two thin strips of metal bonded to a two inch paper tape. To use "flex bead", a worker first spreads all-purpose mud along the wallboard on both sides of the angle. A length of "flex bead" is folded by hand to create a crease. The bead is then installed in the angle. This requires a good eye for straight lines since the "flex bead" will not make a straight line by itself. The worker must move the bead around to the best of his abilities to set it as straight as possible. On many occasions, the worker will end up with a line that is not straight; this condition is called "snaking".
Once the "flex bead" is installed and dry, the first coat procedure is started. Most journeymen only coat one side of the angle at a time. If one tries to coat both sides at the same time, the mud flops over to the other side, and the knife digs a line into the mud on the other side of the angle. Therefore, the following process is usually used: 1) Apply a first coat of mud to one side and wait until it is dry; 2) Apply a first coat of mud to the other side and wait until it is dry; 3) Sand both sides and clean at the crease; 4) Apply a second coat of mud to one side and wait until it is dry; 5) Apply a second coat of mud to the other side and wait until it is dry; 6) Sand and touch up both sides. This process is tedious, and requires considerable time while the respective sides are drying. Accordingly, considerable drawbacks remain unsatisfied.
What is badly needed is a system for finishing drywall on the interior of buildings that avoids the difficulties of taping, corner beads and "flex bead" while retaining the perfect finished appearance that is required for texturing or painting. The sanding steps should be reduced or eliminated. This system should reduce the labor to less than one day for a typical residence and significantly reduce the amount of mud used.